The present invention relates to a rotating impeller for use in mixing vessels. More particularly, the invention pertains to a dual direction, counter flow, impeller that produces flow in two opposite directions.
It is known in many industrial applications to have a mixing vessel that contains a material to be mixed. A rotating shaft extends into the vessel and rotates one or more generally radially extending impellers in order to cause flow in the material to mix the material. Such mixers are used in many industrial and manufacturing applications, including some applications for mixing medium to high viscosity materials. For these materials it is often necessary to perform the mixing in a laminar or transient flow environment. It is desirable to effect a proper mixing, while reducing the amount of energy that needs to be imparted to the material. Reducing the amount of energy imported helps to reduce the mechanical stresses on the impeller, the impeller shaft, and the drive system. Reducing the input energy applied to the material in the regions of the blades can also reduce the shear forces or other undesirable effects that can occur on shear sensitive materials when they are subjected to high shear forces.
One solution to mixing medium and high viscosity materials has been to use a radial impeller that has a blade angled in one direction. The blade extends less than the full radial distance from the shaft to the outside of the tank and pumps the material in one direction, for example, downwardly. Two sets of impeller blades may be disposed at different axial heights on the shaft. This arrangement will push the material in the downward direction in the area radially near the shaft and defined generally by the radial length of the blade. The material then flows horizontally outward at the lower part of the vessel and flows generally upward in a radial area generally between the blade tips of the vessel wall. Upon reaching near the top of the vessel, the material flows radially inwardly and then is pumped downward again by the blades.
A disadvantage of this one-directional blade arrangement is that the energy required for the complete flow cycle is to be applied during only less than half of the flow cycle. In some situations, particularly, for medium and high viscosity materials, this can cause undesirable turbulent flow near the blades, and/or shear effects on the material, and incomplete vessel motion.
Another approach to this problem has been to provide a so-called dual direction impeller which has a first radial segment that pumps fluid in one direction, (e.g., downwardly). Attached at the end of the first segment is a second segment oriented in the other direction that pumps fluid in the other direction (e.g., upwardly). A disadvantage of the known dual direction systems is that because the first segment is connected directly to the second segment, an area of undesirable turbulence and/or radial flow exists in the region where the two blade segments are connected. Turbulence arises because one blade segment is forcing material in one direction and is immediately adjacent to the other segment which is forcing the material in the other direction. Consequently, flow inducing forces are not efficiently transmitted in the region of connection of the two oppositely angled blades. Further, these known arrangements have not taken advantage of the desirable properties that can be gained from using a twisted or curved blade segment.
Accordingly, there is a need in the art for an improved dual direction impeller assembly that can in some embodiments provide improved performance compared to existing dual direction impellers.
It is therefor a feature and advantage of the present invention to provide an improved dual direction impeller assembly that can in some embodiments provide improved performance compared to existing dual direction impellers.
The above and other features and advantages are achieved through the use of a novel dual direction mixing impeller and method as herein disclosed. In accordance with one embodiment of the present invention, an impeller blade for use in a mixing vessel has an inner blade portion angled in a first direction an outer blade portion disposed radially outward from the inner blade portion and a connector element that provides radial spacing between respective inner and outer blade portions.
In accordance with another aspect, an impeller for use in a mixing vessel, has a hub at least two inner blade portions extending from the hub and at least two outer blade portions disposed radially outward from respective inner blade portions. A connector element provides radial spacing between the respective inner and outer blade portions.
In accordance with another aspect, an impeller for use in a mixing vessel has at least two inner blade portions angled in a first direction at least two outer blade portions disposed radially outward from respective inner blade portions, and means for providing radial spacing between the respective inner and outer blade portions.
In accordance with yet another aspect, a method is provided for mixing material in a mixing vessel using an impeller. The method includes the steps of pumping the fluid in a first direction using a blade that extends radially from a hub and forcing the material in a second direction opposite to the first direction using a second blade that is connected to the first blade with a radial space provided between the first and second blades.
There has thus been outlined, rather broadly, the more important features of the invention in order that the detailed description thereof that follows may be better understood, and in order that the present contribution to the art may be better appreciated. There are, of course, additional features of the invention that will be described below and which will form the subject matter of the claims appended hereto.
In this respect, before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein, as well as the abstract, are for the purpose of description and should not be regarded as limiting.
As such, those skilled in the art will appreciate that the conception upon which this disclosure is based may readily be utilized as a basis for the designing of other structures, methods and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention.